Due to the increased demand for highly integrated semiconductor devices, techniques of integrating more semiconductor devices into a smaller area have become strongly relied upon. The integration of many semiconductor devices onto a small area includes downscaling the semiconductor devices to be formed on the semiconductor wafer. Moreover, as the integration density of semiconductor devices increases, the line width and spacing of circuit elements in the semiconductor devices must decrease accordingly.
In general, electronic features of a semiconductor device are formed using patterns created by a photolithography process or processes. Patterns used to form circuit elements with spacing and/or line widths less than a predetermined minimum amount are referred to as “fine pitch” patterns. One of the main factors that determine the minimum pitch of patterns that can be formed by a photolithography process is the type of light source used in the photolithography process. For example, conventional photolithography processes commonly use light sources such as krypton fluoride (KrF) or argon fluoride (ArF) lasers, which have respective wavelengths of 248 nm or 193 nm. Unfortunately, the resolution of these KrF or ArF lasers is not high enough to produce fine pitch patterns required in many advanced semiconductor devices.
Because of this problem, the formation of fine pitch photoresist patterns is currently the subject of much research. One proposed method for forming fine pitch patterns is a double patterning method. Double patterning, or more generally, multiple patterning is a class of technologies developed for photolithography to enhance the feature density. In the semiconductor industry, double patterning may be used as early as the 45 nm node and may be the primary technique for the 32 nm node and beyond.
There are several types of double patterning technologies including, for example, double exposure/double etching or litho-etch-litho-etch (LELE). In such a technique, a first photoresist is first applied to a structure including, from top to bottom, a hard mask, an underlayer and a substrate. After applying the first photoresist to the structure, a first pattern is provided utilizing a conventional lithography step. Following patterning of the first photoresist, the first pattern is transferred to the hard mask utilizing a first etching step that stops on a surface of the underlayer. A second photoresist is then applied to the patterned structure and is exposed to a second patterning step. The second patterning step provides a second pattern into the second photoresist that lies between the first pattern provided in the first patterning and etching step. After second patterning, the second pattern formed in the second photoresist is transferred to the structure utilizing a second etching step. The second etching step removes exposed portions of the hard mask, while also stopping on the surface of the underlayer. The patterned second photoresist is removed and thereafter the first and second patterns provided in the hard mask are transferred to the underlayer utilizing a third etching step.
One problem with conventional double exposure/double etching is that it requires complex processing including the use of two layers of resist and a hard mask. Additionally, many steps are required to deposit and remove the photoresists and hard mask employed in a conventional double exposure/double etching process. Yet another problem with the conventional double patterning techniques is that all the patterns formed are on sacrificial photoresists and/or a hard mask, and, as such, additional etch steps are required to transfer these patterns to the underlying substrate. These transfer steps are costly and often degrade the performance of the underlying structures/devices.
A less complex double patterning method involves direct patterning of two photoresists consecutively. This process is sometime call litho-litho-etch (LLE) double patterning. In this double patterning scheme, a first photoresist is first applied to a structure including, from top to bottom, an antireflective coating and a substrate. After applying the first photoresist to the structure, a first pattern is formed utilizing a conventional lithography step. Following patterning of the first photoresist, a second photoresist is applied directly onto the first patterned photoresist and is subjected to a second patterning step. The second patterning step provides a second pattern into the second photoresist that lies between the first patterned photoresist provided in the first patterning step, thus providing fine pitch (double the resolution) pattern. This fine pitch photoresist pattern is thereafter transferred to the underlying substrate utilizing an etching step.
One of the major problems with this litho-litho-etch double patterning process is the incompatibility of conventional resists. That is, during the double patterning process, the first photoresist dissolves during the formation of the second photoresist, causing deformation of the first pattern.
In view of the above, there is a need for providing a new and improved multiple patterning process in which very small permanent features can be formed which does not require sacrificial photoresists and the etching steps of conventional double patterning processes.